1. Field of the Invention
This invention relates to a vibration driven motor utilizing the ultrasonic vibration of an electro-mechanical energy conversion element such as a piezo-electric element or an electrostrictive element.
2. Related Background Art
Numerous vibration driven motors utilizing the vibration of the aforementioned conversion element have heretofore been proposed. These prior-art motors are such that as shown, for example, in FIGS. 6 and 7 of the accompanying drawings, a rotor 3 is pressed against a stator comprising a ring-like resilient member 1 and piezo-electric ceramics 2 joined thereto, by a pressing spring 5 through a shaft bar 4. The resilient member 1 is supported by a support plate 7 through a vibration insulating member 6 such as felt. The shaft bar 4 is rotatably supported by a bearing 8, and this shaft bar 4 and the rotor 3 are integrally coupled together and therefore, the rotor 3 can rotate about the shaft bar 4 without contacting the latter. When AC electric fields of two phases which are .pi./2 out of phase with each other in time are applied from a driving circuit, not shown, to the piezo-electric ceramics 2 disposed with a spatial phase difference therebetween, a travelling vibration wave is generated in the stator and the rotor 3 is rotated in the direction opposite to the direction of travel of the vibration wave by the frictional force thereof with the stator.
The resilient member 1 has a number of slits 1a formed at equal or unequal intervals on the sliding surface side thereof which is in contact with the rotor 3 to improve the efficiency of the motor. As the material of the resilient member 1 comprising the slits 1a, a base body 1b and projections 1c, use has been made of a metal which is small in the energy loss by vibration (a metal which is small in vibration attenuation), for example, stainless steel, carbon steel, brass, phosphor bronze or the like.
Such a shape and material of the resilient member 1 are considered to be indispensable conditions in designing a vibration driven motor of high performance.
Heretofore, the slits 1a provided in this resilient member 1 have been formed one by one by machining and cutting, and this has led to the problem that the working cost of the resilient member 1 is increased and the cost of the vibration driven motor or actuator is also increased.
In order to solve this problem, it has been proposed to form the resilient member 1 by the forging method.
However, this forging method has a limitation in forming the slits 1a with the pitch and depth thereof stabilized, and it has been difficult to form the shape of the slits at a stroke by forging because it is impossible to form the number and depth of slits great enough to maintain the motor performance now demanded and because stainless steel or brass suited for the vibration member is a material unsuited for forging although a material rich in malleability is required in forging.